Question: I disassembled some old pc’s of mine, and I’d like to use the space on their hard drives for my current pc. The old pc’s run windows 7 and still have the os and files installed on the drives. I was wondering if it would work to simply plug the old drives into my windows 10 pc and clear them once it opened? Or would there be some kind of conflict between the different versions/hard drives?

Answer:Yes.
You should be OK.

As above…if it looks like a Windows 7 booting up, things went wrong…